OFFSET
0,3
FORMULA
Euler transform of period 20 sequence [ -1, -2, -1, -1, -2, -2, -1, -1, -1, 0, -1, -1, -1, -2, -2, -1, -1, -2, -1, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (80 t)) = 20^(1/2) g(t) where q = exp(2 Pi i t) and g() is g.f. for A144724.
EXAMPLE
1/q - q^3 - 2*q^7 + q^11 + q^15 + 3*q^27 + q^31 - 3*q^35 - q^39 + ...
PROG
(PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A) * eta(x^2 + A) * eta(x^5 + A) * eta(x^20 + A) / (eta(x^4 + A) * eta(x^10 + A)^3), n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Nov 10 2008
STATUS
approved